Preparation method of isotropic modified graphite negative electrode material for high-rate lithium ion battery

Abstract

This invention relates to the field of lithium-ion battery anode material technology, and particularly to a method for preparing isotropic modified graphite anode materials for high-rate lithium-ion batteries, comprising: Step 1: raw material pretreatment and primary isotropic shaping; Step 2: multi-stage spray granulation and pore structure control; Step 3: preparation and application of composite coating layer; Step 4: fusion heat treatment and interface strengthening; Step 5: surface stabilization and carbonization treatment, wherein the graphite particles obtained in Step 4 are mixed with a carbon precursor solution, and the carbon precursor solution is uniformly coated on the surface of the graphite particles using a fluidized bed apparatus, followed by carbonization treatment under an inert atmosphere, controlling the carbonization temperature to be lower than the graphitization temperature, so that the carbon precursor is transformed into an amorphous carbon layer, forming an amorphous carbon protective layer on the surface. Through carbonization treatment and the strengthening of the composite coating layer, the material possesses high chemical stability and good thermal stability, greatly improving the safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a method for preparing isotropic modified graphite anode materials for high-rate lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as a new generation of energy storage devices, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems. With the rapid development of the electric vehicle industry, higher demands are being placed on the fast-charging capabilities of lithium-ion batteries. As a core component of lithium-ion batteries, the performance of the anode material directly determines the battery's fast-charging performance, cycle life, and safety performance.

[0003] Existing methods for preparing isotropic graphite anode materials still have many shortcomings: the degree of isotropy is limited, making it difficult to achieve truly uniform lithium-ion insertion and extraction; there is a contradiction between rate performance and cycle stability, and improving fast charging capability often comes at the cost of cycle life; the preparation process is complex and costly, making it difficult to meet industrialization needs; and the material structure design is not reasonable enough to simultaneously solve the problems of ion transport, electronic conductivity, and structural stability.

[0004] Therefore, developing a method for preparing isotropic modified graphite anode materials that can meet the requirements of high-rate charge and discharge while also possessing excellent cycle stability and safety has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To achieve the above objectives, this invention provides a method for preparing isotropic modified graphite anode materials for high-rate lithium-ion batteries, comprising the following steps:

[0006] Step 1: Raw material pretreatment and primary isotropic shaping. Natural flake graphite or artificial graphite is selected as raw material. The graphite raw material is mixed with deionized water to form a slurry. The graphite raw material is sheared by mechanical fluid shearing equipment. The shearing intensity and time are controlled to make the aspect ratio of the graphite particles approach 1, thus achieving primary isotropic shaping. Subsequently, the treated graphite slurry is subjected to solid-liquid separation and drying to obtain the primary isotropic graphite intermediate.

[0007] Step 2: Multi-stage spray granulation and pore structure control. The primary isotropic graphite intermediate obtained in Step 1 is mixed with the binder solution to form a uniform suspension. The suspension is then treated using a multi-stage spray granulation device, which includes a first-stage spray unit to form micron-sized droplets, a second-stage spray unit to introduce a pore template agent onto the droplet surface, and a third-stage spray unit to cover the droplet with an outer protective film. Subsequently, a programmed temperature heat treatment is performed under an inert atmosphere. The programmed temperature heat treatment includes first heating at a slow rate to a low temperature zone to partially cross-link and solidify the binder, then heating at a faster rate to a medium temperature zone to remove the pore template agent and form a porous structure, and finally, completely carbonizing the binder in a high temperature zone to form secondary spherical graphite particles with internal porous channels and a dense outer shell.

[0008] Step 3: Preparation and application of composite coating layer. A composite coating material composed of conductive carbon material and tin-based alloy is prepared. The conductive carbon material is selected from graphene, carbon nanotubes or porous carbon. The tin-based alloy is a binary or ternary alloy of tin with copper, silver or antimony. First, the tin-based alloy material and conductive carbon material are mixed in proportion. Under the protection of inert gas, the mixture is heated to above the melting point of the tin-based alloy and kept warm while stirring to allow the liquid alloy to fully wet the conductive carbon material. After cooling, the composite coating material is obtained. Then, the secondary spherical graphite particles obtained in step 2 are mixed with the composite coating material in proportion. The composite coating material is uniformly attached to the surface of the secondary spherical graphite particles by a high-speed impact mixing device.

[0009] Step 4: Fusion heat treatment and interface strengthening. The coated graphite particles obtained in Step 3 are subjected to fusion heat treatment in a multi-temperature zone tube furnace under inert atmosphere protection. First, the temperature is raised to the first temperature zone at a medium heating rate and held to allow the low-melting-point components in the composite coating to partially melt and form a preliminary bond with the surface of the graphite particles. Then, the temperature is raised to the second temperature zone at a slower heating rate and held to the second temperature zone. The second temperature zone is higher than the melting point of tin-based alloys but lower than the graphitization temperature, allowing the composite coating to form a strong bond with the surface of the graphite particles through interfacial diffusion. Finally, the temperature is cooled to room temperature at a controlled cooling rate.

[0010] Step 5: Surface stabilization and carbonization treatment. The graphite particles obtained in Step 4 are mixed with the carbon precursor solution. A fluidized bed apparatus is used to uniformly coat the surface of the graphite particles with the carbon precursor solution. Then, carbonization treatment is carried out under an inert atmosphere. The carbonization temperature is controlled to be lower than the graphitization temperature, so that the carbon precursor is transformed into an amorphous carbon layer, forming an amorphous carbon protective layer on the surface.

[0011] Preferably, in step one, the mechanical fluid shearing device includes a rotor-stator shearing head. The rotor rotates at a high speed, generating strong fluid shearing force and turbulence effect within a narrow gap. The temperature of the slurry is controlled within a certain range by an external cooling or heating system. The viscosity of the slurry is controlled by adjusting the solid content. The aspect ratio of the graphite particles is controlled by adjusting the shearing time, rotor speed, and slurry concentration. During the process, a rheometer is used to monitor the changes in the rheological properties of the slurry in real time. Shearing is stopped when the slurry changes from obvious shear-thinning behavior to near-Newtonian fluid behavior. The graphite is then separated into solid and liquid phases using a centrifuge or filter. The separated solid is dried in a vacuum drying oven at a temperature controlled to prevent graphite oxidation, yielding a primary isotropic graphite intermediate. The shear head of the mechanical fluid shearing device generates a high-speed turbulent flow field, causing relative slippage and randomization of the orientation of the graphite particles. The shearing time is adjusted based on the initial anisotropy of the graphite raw material. For natural flake graphite, the shearing time is longer to fully destroy its flake structure, while for artificial graphite, the shearing time is shorter to optimize the isotropic effect.

[0012] Preferably, in step two, the first-stage spray unit of the multi-stage spray granulation equipment uses pressure nozzles to atomize the suspension into micron-sized droplets. The droplet size is controlled by adjusting the nozzle orifice diameter and the feed pressure. The second-stage spray unit is located 0.5-1.0 meters downstream of the first-stage spray unit and is used to uniformly spray a pore template agent solution onto the droplet surface. The pore template agent is an organic or inorganic salt that can be decomposed and removed during heat treatment. The third-stage spray unit further coats the droplet surface with a protective polymer solution to prevent the structure formed in the first two stages from being destroyed in subsequent processing. The specific process of the programmed temperature rise heat treatment includes: a first stage with a heating rate of 1-5 degrees Celsius per minute. The temperature is raised to 100-150 degrees Celsius and held for 30-60 minutes to partially cross-link and cure the binder. In the second stage, the temperature is raised to 300-400 degrees Celsius at a rate of 5-10 degrees Celsius per minute and held for 60-120 minutes to decompose and volatilize the pore template agent, forming a porous structure. In the third stage, the temperature is raised to 600-800 degrees Celsius at a rate of 10-15 degrees Celsius per minute and held for 120-180 minutes to completely carbonize the binder and form a carbonaceous skeleton. The binder is a thermoplastic polymer material, which undergoes softening, flow, and final carbonization during heating. The solid content in the suspension is controlled between 10% and 30% to ensure smooth spray granulation.

[0013] Preferably, in step three, the preparation process of the composite coating material includes: first, mixing tin-based alloy powder and conductive carbon material at a mass ratio of 1:1 to 3:1, mixing under an inert gas atmosphere to prevent oxidation of the material; placing the uniformly mixed powder in a reactor under vacuum or inert atmosphere protection, heating it to 50-100 degrees Celsius above the melting point of the tin-based alloy at a heating rate of 2-8 degrees Celsius per minute, holding it at this temperature for 30-90 minutes with continuous stirring, so that the molten tin-based alloy fully wets the pores and surface of the conductive carbon material; and then cooling it at a cooling rate of 1-5 degrees Celsius per minute. The composite coating material is obtained by cooling to room temperature. The mixing process of the high-speed impact mixer includes: mixing secondary spherical graphite particles and the composite coating material at a mass ratio of 10:1 to 5:1, and placing them into the high-speed impact mixer. The mixer uses high-speed rotating blades to generate strong impact and shearing action, controlling the rotation speed at 500-2000 rpm, the mixing time at 10-30 minutes, and the mixing temperature at 25-60 degrees Celsius, to ensure that the composite coating material is uniformly and firmly attached to the surface of the secondary spherical graphite particles without damaging the overall structure of the secondary spherical graphite particles.

[0014] Preferably, in step four, the multi-zone tubular furnace for the fusion heat treatment has three independently controlled temperature zones. High-purity inert protective gas is continuously introduced into the furnace, with the gas flow rate controlled at 0.5-2.0 liters / minute to prevent material oxidation. The first temperature zone is 200-300 degrees Celsius, with a holding time of 30-60 minutes, allowing the low-melting-point components in the composite coating to partially melt and undergo preliminary interfacial reactions and atomic diffusion with the graphite particle surface. The second temperature zone is 400-500 degrees Celsius, with a holding time of 120-240 minutes, allowing the molten tin-based alloy to fully contact the graphite particle surface and form a strong metallurgical bond through interfacial diffusion. Simultaneously, the conductive carbon material acts as a buffer matrix to suppress excessive flow and aggregation of the tin-based alloy. The controlled cooling rate is slowly reduced to room temperature at a rate of 0.5-2 degrees Celsius per minute to avoid interfacial cracking or coating layer detachment caused by thermal stress generated by rapid cooling. During the fusion heat treatment, the bonding phase formed at the interface is stably solidified, forming a gradient transition interface structure.

[0015] Preferably, in step five, the carbon precursor solution is a phenolic resin solution, a sugar solution, or an asphalt solution, and the carbon precursor can form a dense amorphous carbon layer after heat treatment; the operating conditions of the fluidized bed equipment include: airflow velocity controlled at 0.1-0.5 m / s, temperature controlled at 50-80 degrees Celsius, so that the graphite particles are in full contact with the carbon precursor solution in a fluidized state, ensuring that the solution is uniformly coated on the particle surface; the specific process of the carbonization treatment includes: first heating to 200-300 degrees Celsius at a heating rate of 1-3 degrees Celsius per minute. The carbon precursor is partially cross-linked and cured at 00 degrees Celsius for 60-120 minutes to form a stable temporary protective layer. Then, the temperature is increased to 500-700 degrees Celsius at a rate of 3-6 degrees Celsius per minute and held for 120-180 minutes to transform the carbon precursor into an amorphous carbon layer. The carbonization temperature is lower than the graphitization temperature to avoid damaging the already formed composite structure. The amorphous carbon layer fills the micropores and defects on the surface of the composite coating layer to form a dense protective layer, and at the same time, it forms a strong bond with the underlying composite coating layer through carbon atom diffusion.

[0016] Preferably, the preparation method further includes performance testing of the final isotropic modified graphite anode material, including electrochemical performance testing and physical performance testing; the electrochemical performance testing is conducted using coin cells, and the test content includes initial coulombic efficiency, reversible specific capacity, rate capacity retention, and cycle capacity retention; the physical performance testing includes observing the microstructure of the material using scanning electron microscopy, analyzing the crystal structure of the material using X-ray diffraction, and analyzing the pore characteristics of the material using specific surface area and porosity; the process parameters in the preparation method are adjusted based on the performance test results to optimize the material performance.

[0017] Preferably, in step one, the particle size distribution of the graphite raw material is controlled within the range of 5-50 micrometers, and the solid content of the slurry is controlled between 15% and 25%; in step two, the binder is one of polyvinyl alcohol, polyacrylic acid, or polyurethane, and the mass fraction of the binder in the suspension is 5%-15%; in step three, the specific surface area of ​​the conductive carbon material is controlled within 100-500 square meters per gram, and the particle size distribution of the tin-based alloy is controlled within 0.1-5 micrometers; in step four, the inert protective gas used in the inert atmosphere is argon or nitrogen, and the gas purity is not less than 99.99%; in step five, the mass fraction of the carbon precursor solution is 10%-20%, and the thickness of the amorphous carbon layer after carbonization is controlled within 10-100 nanometers.

[0018] Preferably, the control of all process parameters in the preparation method is based on real-time monitoring and feedback adjustment. In step one, the rheological properties of the slurry are monitored in real time using an online rheometer, and the shearing time and rotor speed are dynamically adjusted according to the monitoring results. In step two, the droplet size distribution during spray granulation is monitored in real time using a laser particle size analyzer, and the nozzle parameters and feed pressure are adjusted according to the monitoring results. In step three, the temperature distribution during the mixing process is monitored in real time using an infrared thermal imager, and the mixing speed and time are adjusted according to the monitoring results. In step four, the temperature and atmosphere composition during the heat treatment process are monitored in real time using a thermocouple and a gas analyzer, and the heating rate and gas flow rate are adjusted according to the monitoring results. In step five, the amount of solution adsorbed during the coating process is monitored in real time using a weight sensor, and the fluidized bed operating conditions are adjusted according to the monitoring results.

[0019] Preferably, the isotropic modified graphite anode material obtained by the preparation method has multiple structural features: an isotropic graphite core, an intermediate composite coating layer, and a surface amorphous carbon protective layer. The aspect ratio of the isotropic graphite core is controlled between 1.0 and 1.2 to achieve high isotropy. The thickness of the intermediate composite coating layer is controlled between 0.5 and 5 micrometers, providing high electronic conductivity and buffering effect. The thickness of the surface amorphous carbon protective layer is controlled between 10 and 100 nanometers, improving the chemical stability and structural integrity of the material surface. The isotropic modified graphite anode material exhibits a capacity retention rate of not less than 95% at 2C, not less than 85% at 5C, and a capacity retention rate of not less than 97% after 500 cycles, with an electrode expansion rate not exceeding 8%. Beneficial effects of the present invention:

[0020] 1. Through multi-stage isotropic treatment, graphite particles achieve high isotropy in microstructure, allowing lithium ions to be inserted and extracted simultaneously from multiple directions, significantly improving ion transport rate and rate performance.

[0021] 2. The secondary spherical particle structure with a porous interior and a dense outer shell provides abundant transport channels for lithium ions while maintaining the structural integrity of the particles, effectively suppressing side reactions of the electrolyte and graphite layer peeling.

[0022] 3. By designing a tin-based alloy-carbon composite coating layer, the high capacity and good conductivity of the tin-based alloy are used to improve the overall performance of the composite material. At the same time, the buffering effect of the carbon material suppresses the volume effect of the tin-based alloy, thereby improving the cycle stability of the material.

[0023] 4. Through a multi-stage fusion heat treatment process, a strong bond was achieved between the composite coating layer and the graphite matrix, forming a stable interface structure and avoiding the problem of coating layer detachment during cycling.

[0024] 5. The use of secondary carbon coating technology further improves the chemical stability and structural integrity of the material surface, reduces side reactions with the electrolyte, and improves the initial coulombic efficiency. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the steps of the method of the present invention;

[0027] Figure 2 This is a flowchart illustrating the steps involved in preparing the composite coating material of the present invention.

[0028] Figure 3 This is a flowchart illustrating the mixing process of the high-speed impact mixing device of the present invention. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0030] Please see Figures 1-3 This invention provides a method for preparing isotropic modified graphite anode materials for high-rate lithium-ion batteries. In step 1, natural flake graphite or artificial graphite is first selected as raw material and subjected to preliminary shearing. The shearing intensity and time are controlled using a mechanical fluid shearing device to make the aspect ratio of the graphite particles close to 1, thereby achieving preliminary isotropy. This step optimizes the morphology of the graphite particles, making them more uniform in shape, providing a foundation for subsequent high-rate charge-discharge performance. It improves the lithium-ion insertion and extraction efficiency, ensuring greater stability and efficiency of the battery during high-rate charge-discharge processes.

[0031] Step 2 involves mixing a primary isotropic graphite intermediate with a binder solution and then spray-granulating the mixture using a multi-stage spray granulation device. The device's three-stage spray unit forms micron-sized droplets and introduces a pore-templating agent, thereby creating a porous structure within the graphite particles while simultaneously forming a dense protective shell on the outer layer. The pore-templating agent is then removed through programmed temperature heat treatment, yielding secondary spherical graphite particles with a well-developed porosity. This step effectively improves the ion transport performance of the graphite particles and increases the specific surface area of ​​the material through the introduction of pores, thus enhancing the cycle stability of the battery.

[0032] In step 3, a conductive carbon material and a tin-based alloy (such as an alloy of tin with copper, silver, or antimony) are mixed and heated above their melting point, allowing the liquid alloy to fully wet the conductive carbon material. Then, the coating material is uniformly attached to the surface of the secondary spherical graphite particles. The introduction of the tin-based alloy improves the conductivity of the graphite anode material and effectively prevents increased resistance due to excessive current density during high-rate charging and discharging. Furthermore, conductive carbon materials such as graphene, carbon nanotubes, or porous carbon further enhance the electronic conductivity of the material, improving the battery's fast-charging capability.

[0033] In step 4, the composite-coated graphite particles undergo a multi-stage temperature-zone fusion heat treatment under an inert atmosphere. This treatment first allows the low-melting-point components in the composite coating to form a preliminary bond with the graphite particle surface. Then, through diffusion in the high-temperature zone, a strong bond is formed between the coating and the graphite particle surface. This step ensures a strong interfacial bond between the composite coating material and the graphite anode, improving the structural stability and cycle life of the material during charge and discharge. By controlling the cooling rate, the bond between the coating and the graphite particles can be prevented from loosening, further enhancing the overall performance of the battery.

[0034] In step 5, the graphite particles, after undergoing fusion heat treatment, are mixed with the carbon precursor solution and uniformly coated in a fluidized bed apparatus. Through carbonization, the carbon precursor is transformed into an amorphous carbon layer, forming a protective layer on the surface. This amorphous carbon protective layer not only provides additional conductivity but also effectively reduces the surface energy of the graphite particles, improving the chemical stability of the material and thus enhancing battery safety. This step ensures that the battery performance will not degrade due to changes in the external environment (such as temperature fluctuations, humidity, etc.) during use.

[0035] Through meticulous design and multi-step processing technology, several problems of isotropic graphite anode materials in existing technologies have been solved, and the overall performance of high-rate lithium-ion batteries has been significantly improved, showing broad application prospects.

[0036] In one possible implementation, the mechanofluidic shearing device generates intense shearing forces and turbulence effects within the narrow gap between the rotor and stator through a high-speed rotating rotor. The high-speed rotation of the rotor creates a strong shear force field in the slurry, causing relative slippage and randomization of the orientation of the graphite particles. This effectively breaks down the original lamellar structure of the graphite particles and optimizes their isotropy, resulting in higher ionic conductivity and stronger structural stability for subsequent battery applications.

[0037] The temperature of the slurry is controlled within a suitable range by using an external cooling or heating system to avoid excessively high temperatures that could lead to graphite oxidation or adverse shearing effects.

[0038] By adjusting the solids content in the slurry, the viscosity of the slurry can be controlled, thereby regulating the shearing effect. The viscosity of the slurry directly affects the shearing behavior and morphology of graphite particles; therefore, optimizing the solids content can achieve the best shearing effect.

[0039] The adjustment of shearing time, rotor speed, and slurry concentration is to precisely control the aspect ratio (i.e., the shape of the graphite particles). By reasonably adjusting the shearing time and speed, the shearing process can be optimized according to the initial morphology of the graphite raw material. For example, for natural flake graphite, a longer shearing time is required to fully break down its flake structure, making its morphology tend towards spherical or near-spherical shapes; while for artificial graphite, a shorter shearing time is needed to avoid over-shearing and destroying its good isotropic effect.

[0040] Throughout the shearing process, the rheological properties of the slurry were monitored in real time using a rheometer. When the slurry's flow behavior shifted from significant shear-thinning to near-Newtonian fluid behavior, it indicated that the shearing treatment had reached its optimal effect, and the treatment was stopped at this point. This precise control ensured that the morphology and properties of the graphite particles were optimally optimized throughout the entire process.

[0041] After shearing, solid-liquid separation is performed using a centrifuge or filter to separate the solids from the slurry, yielding a primary isotropic graphite intermediate. The separated solids are then dried in a vacuum drying oven, with the drying temperature controlled within a specific range to prevent graphite oxidation or other adverse changes. The resulting intermediate exhibits excellent morphology and stability, providing a good foundation for subsequent processing steps.

[0042] By precisely controlling the mechanical fluid shearing process, the morphology of graphite particles was optimized and made isotropic, which improved the performance of the anode material in high-rate lithium-ion batteries. Furthermore, this process has high adaptability, controllability, and economy.

[0043] In one possible implementation, the first-stage spray unit atomizes the suspension into micron-sized droplets using pressure nozzles. The droplet size can be precisely controlled by adjusting the nozzle orifice diameter and feed pressure, ensuring uniform size and distribution of each droplet, thus laying the foundation for subsequent processing. The droplet size directly affects the structure and surface properties of the final particles; controlling its size contributes to the formation of high-quality materials.

[0044] The second-stage spray unit: At a specific location downstream of the first-stage spray unit, a pore-templating agent solution is uniformly sprayed onto the droplet surface. The pore-templating agent can be an organic or inorganic salt that can be decomposed and removed during high-temperature processing, thereby forming a pore structure. The key to this step is to ensure that the template agent uniformly covers the surface of each droplet to form a good porous structure, thereby optimizing the electrochemical performance of the graphite particles.

[0045] The third-stage spray unit further coats the droplet surface with a protective polymer solution. This protective film prevents damage to the structure formed in the first two stages during subsequent heat treatment. The protective coating provides structural support to the droplet, preventing structural collapse due to temperature changes or chemical reactions during heat treatment.

[0046] Programmed heating heat treatment:

[0047] First stage: Heat the particles to 100-150 degrees Celsius and maintain this temperature for 30-60 minutes. This stage mainly involves partially cross-linking and curing the binder, enhancing the initial structural stability of the particles.

[0048] The second stage involves raising the temperature to 300-400 degrees Celsius at a rate of 5-10 degrees Celsius per minute and maintaining this temperature for 60-120 minutes. The key to this stage is the decomposition and volatilization of the pore template agent, which removes and forms a porous structure, thereby increasing the specific surface area of ​​the graphite material and the battery's capacity.

[0049] The third stage involves raising the temperature to 600-800 degrees Celsius at a rate of 10-15 degrees Celsius per minute and holding it at that temperature for 120-180 minutes to completely carbonize the binder and form a robust carbonaceous skeleton. This stage is crucial for ensuring the material exhibits good electrical conductivity and structural stability.

[0050] Throughout the preparation process, the solid content in the suspension was controlled between 10% and 30%. Appropriate solid content ensured the smooth operation of the spray granulation process and effectively controlled the size and morphology of the particles.

[0051] By combining multi-stage spray granulation with fine heat treatment, the morphology, pore structure, and electrochemical performance of graphite particles have been successfully optimized, providing a high-quality anode material for high-rate lithium-ion batteries. This method boasts high production efficiency, good particle stability, and excellent battery performance, meeting the demands of high-performance batteries.

[0052] In one possible implementation, tin-based alloy powder is first mixed with conductive carbon material at a mass ratio of 1:1 to 3:1. The tin-based alloy is used in this invention to enhance the conductivity and cycle stability of the graphite anode material, while the conductive carbon material provides the necessary electrical conductivity and structural stability. This mixing process needs to be carried out under an inert gas atmosphere to prevent oxidation of the raw materials at high temperatures, ensuring the purity and performance of both the alloy powder and the carbon material.

[0053] The uniformly mixed powder is placed in a reactor under vacuum or inert atmosphere protection and heated to 50-100 degrees Celsius above the melting point of the tin-based alloy at a heating rate of 2-8 degrees Celsius per minute, and held at this temperature for 30-90 minutes. The goal of this stage is to allow the molten tin-based alloy to completely penetrate the pores and surface of the conductive carbon material, ensuring that the tin-based alloy can fully bond with the carbon material to form a composite coating layer with excellent electrical conductivity.

[0054] After the molten alloy infiltration process is completed, the temperature is gradually reduced to room temperature at a cooling rate of 1-5 degrees Celsius per minute to complete the preparation of the composite coating material. This cooling process can prevent material brittleness or structural inhomogeneity caused by excessively rapid cooling, ensuring the stability and structural integrity of the composite material.

[0055] The prepared composite coating material is mixed with secondary spherical graphite particles at a mass ratio of 10:1 to 5:1. This step requires ensuring that the composite coating material adheres uniformly to the surface of the graphite particles without damaging the overall structure of the graphite particles. Secondary spherical graphite particles possess good mechanical strength and excellent electrochemical performance, making them ideal anode materials for high-rate lithium-ion batteries.

[0056] The mixture is placed in a high-speed impact mixer, which generates strong impact and shearing forces through high-speed rotating blades. The rotation speed is controlled at 500-2000 rpm, the mixing time at 10-30 minutes, and the mixing temperature at 25-60 degrees Celsius. High-speed impact mixing effectively ensures that the composite coating material is uniformly distributed on the surface of the graphite particles, and the precise adjustment of temperature and mixing time avoids the destruction of graphite particle morphology caused by over-stirring.

[0057] This invention significantly improves the conductivity, stability, and mechanical strength of graphite anode materials by precisely controlling the preparation process and mixing process of composite coating materials, enabling them to have excellent performance in high-rate lithium-ion batteries.

[0058] In one possible implementation, a multi-zone tube furnace is used, featuring three independently controlled temperature zones to precisely control the heating process at different stages. A high-purity inert protective gas (such as nitrogen or argon) is continuously introduced into the furnace, with the gas flow rate strictly controlled between 0.5 and 2.0 liters per minute. This is to ensure the stability of the composite coating material during heating, prevent oxygen from reacting with the material, avoid oxidation, and guarantee the purity and performance of the final product.

[0059] The first temperature range: Within the temperature range of 200-300 degrees Celsius, the material is held at this temperature for 30-60 minutes. The main purpose of this stage is to partially melt the low-melting-point components in the composite coating layer, thereby initiating an interfacial reaction with the graphite particle surface. Low-melting-point metals (such as tin-based alloys) begin to penetrate the graphite particle surface during this stage, promoting atomic-level diffusion, thus laying the foundation for subsequent metallurgical bonding.

[0060] The second temperature range involves raising the temperature to 400-500 degrees Celsius and maintaining this range for 120-240 minutes. During this time, the molten tin-based alloy comes into full contact with the graphite particle surface, forming a strong metallurgical bond through interfacial diffusion. This stage is crucial because it not only strengthens the bond between the tin-based alloy and the graphite particles but also prevents excessive flow and aggregation of the tin-based alloy through the conductive carbon material acting as a buffer matrix, ensuring the uniformity and stability of the alloy layer.

[0061] After the high-temperature treatment, strict cooling rate control was employed to prevent interface cracking or coating delamination caused by thermal stress from rapid cooling. The cooling rate was controlled between 0.5 and 2 degrees Celsius per minute, slowly reducing the temperature to room temperature. Slow cooling effectively avoids cracks or interface instability caused by thermal stress, helping to maintain the integrity of the composite coating.

[0062] During the entire heat treatment process, the bonding phase formed between the composite coating layer and the graphite particle surface will stabilize and solidify, gradually forming a gradient transition interface structure. This gradient transition interface structure can effectively buffer the volume change between the graphite particles and the tin-based alloy, prevent stress concentration caused by differences in thermal expansion, thereby improving the mechanical strength and cycle stability of the anode material.

[0063] The fusion heat treatment process, through precise temperature and atmosphere control, ensures a good bond between the composite coating material and the graphite particles, which not only improves the electrochemical performance of the material, but also enhances its mechanical strength and cycle life.

[0064] In one possible implementation, the choice of carbon precursor solution is crucial for the formation of the amorphous carbon layer. Materials such as phenolic resin solutions, sugar solutions, or asphalt solutions can be used. These carbon precursor solutions can be transformed into a dense amorphous carbon layer during heat treatment, filling microscopic pores and defects on the surface of graphite particles, thereby enhancing the stability of the graphite particles and providing protection. Under certain conditions, these carbon precursor solutions can be uniformly distributed on the surface of graphite particles, ensuring the formation of a high-quality amorphous carbon layer.

[0065] A fluidized bed coating process is employed to coat graphite particles, ensuring that the carbon precursor solution fully contacts the surface of the graphite particles. During fluidized bed operation, the airflow velocity is controlled between 0.1 and 0.5 m / s, and the temperature is maintained between 50 and 80 degrees Celsius. This temperature range effectively prevents overheating of the graphite particles while ensuring uniform coating of the carbon precursor solution onto their surface. The airflow in the fluidized bed allows the graphite particles to flow freely in suspension, thereby ensuring the uniformity of the coating process.

[0066] After coating in the fluidized bed apparatus, the graphite particles enter the carbonization stage. Temperature control during carbonization is crucial. First, the temperature is increased to 200-300 degrees Celsius at a rate of 1-3 degrees Celsius per minute and held for 60-120 minutes to partially crosslink and solidify the carbon precursor, forming a stable temporary protective layer. Next, the temperature is increased to 500-700 degrees Celsius at a rate of 3-6 degrees Celsius per minute and held for 120-180 minutes. At this point, the carbon precursor transforms into an amorphous carbon layer. Since the carbonization temperature is lower than the graphitization temperature, this process avoids damaging the already formed composite structure.

[0067] During the carbonization process, the carbon precursor is transformed into an amorphous carbon layer, filling the microscopic pores and defects on the surface of the graphite particles to form a dense protective layer. This amorphous carbon layer not only enhances the surface structure of the graphite particles but also provides additional mechanical protection, preventing damage or structural instability during use. Simultaneously, this carbon layer forms a strong bond with the underlying composite coating layer through carbon atom diffusion, ensuring the stability and electrochemical performance of the entire composite structure.

[0068] By precisely selecting carbon precursor solutions, fluidized bed coating, and carbonization processes, the electrochemical and mechanical properties of high-rate lithium-ion battery anode materials can be effectively improved, providing a more stable service life and higher charge-discharge efficiency.

[0069] In one possible implementation, electrochemical performance testing is primarily conducted using coin cells, a standard small battery testing device capable of accurately measuring the electrochemical behavior of the negative electrode material. The testing includes:

[0070] First-cycle coulombic efficiency: The energy conversion efficiency of a battery during the first charge and discharge cycle, typically reflecting the irreversible capacity loss of the material during the first cycle. A high first-cycle coulombic efficiency indicates good structural stability of the material.

[0071] Reversible specific capacity refers to a material's ability to retain capacity during multiple charge-discharge cycles, characterizing its stability and long-term performance. A higher specific capacity indicates stronger electrochemical stability and a longer battery life.

[0072] Rate capacity retention: This test evaluates the material's performance at different discharge rates through charge-discharge processes at varying rates. High rate capacity retention indicates that the material can effectively maintain its capacity during high-rate charge-discharge processes, meeting high power demands.

[0073] Cycle capacity retention: This refers to the percentage of capacity that a material retains after multiple charge-discharge cycles. A high cycle capacity retention means that the material can maintain a high capacity after many cycles and is not easily degraded.

[0074] Physical performance testing primarily focuses on the microstructure and physical properties of materials, and the testing content includes:

[0075] Scanning electron microscopy (SEM) observation: SEM is used to observe the microstructure and surface structure of materials, analyze particle distribution, morphology, and whether there are cracks or inhomogeneities. A good microstructure helps improve the electrical conductivity and mechanical strength of materials.

[0076] X-ray diffraction (XRD) analysis: XRD technology is used to analyze the crystal structure of materials, understand their crystal arrangement and phase composition. This helps determine the crystallinity of graphite materials and whether there are unstable phases that affect the electrochemical performance of the materials.

[0077] Specific surface area and porosity analysis: Specific surface area and porosity are important indicators for evaluating the pore characteristics of materials. A larger specific surface area and appropriate porosity facilitate the contact between the electrolyte and the material, improve ion conduction performance, and thus enhance the battery's capacity and rate performance.

[0078] The test results of the above electrochemical and physical properties can reveal the material's performance under different conditions, allowing for adjustments to key parameters in the preparation process. For example, if the initial coulombic efficiency is low, it may be necessary to optimize the selection of the carbon precursor and the carbonization temperature; if the rate capacity retention is unsatisfactory, it may be necessary to adjust the fluidized bed coating conditions or optimize the morphology of the graphite particles. By analyzing the test results, the process conditions at each step can be further optimized, ensuring that the final isotropic modified graphite anode material achieves optimal electrochemical performance, mechanical properties, and long-term stability.

[0079] In one possible implementation, the preparation process first requires selecting a suitable graphite raw material and controlling its particle size distribution within the range of 5-50 micrometers. This particle size range helps improve the electrochemical performance of the graphite anode, especially during high-rate discharge, effectively increasing the ion diffusion rate, reducing the battery's internal resistance, and thus improving the battery's rate performance. Simultaneously, the solid content of the slurry is controlled between 15% and 25%. This controlled range helps obtain good slurry flowability and adhesion, avoiding an excessively thin or thick slurry during preparation, which would affect subsequent coating and drying processes. The stability of the slurry is crucial for the film quality and the stability of battery performance.

[0080] The selected binder is one of polyvinyl alcohol, polyacrylic acid, or polyurethane. These binders possess good adhesion and appropriate thermal stability, which helps improve the mechanical strength of the graphite anode material and prevents electrode material detachment or pulverization during use. The mass fraction of the binder in the suspension is controlled between 5% and 15%. This ratio ensures that the binder can fully exert its binding effect without excessively affecting the electrochemical performance of the graphite material, thus avoiding a decline in battery performance due to excessive binder usage.

[0081] The specific surface area of ​​the conductive carbon material is controlled between 100-500 m² / g. This range ensures a sufficiently large contact area between the carbon material and the electrolyte, thereby improving the battery's conductivity and enhancing its performance at high rates. The particle size distribution of the tin-based alloy is controlled between 0.1-5 micrometers. This particle size range helps improve the material's conductivity while avoiding a decline in battery cycle performance due to excessively large particle sizes. Tin-based alloys can effectively improve the reversible capacity of graphite anodes, especially enhancing the material's stability during long-term cycling.

[0082] The choice of inert protective gas is crucial during the carbonization process; argon or nitrogen are typically used, with a purity requirement of no less than 99.99%. These inert gases effectively prevent the material from reacting with oxygen or moisture during high-temperature processing, avoiding the formation of undesirable oxides or impurities, thus ensuring the purity and high performance of the graphite anode material. Furthermore, the use of inert gases provides a favorable atmospheric environment, which helps control the temperature and reaction rate during the carbonization process.

[0083] The mass fraction of the carbon precursor solution is controlled between 10% and 20% to ensure that the carbon precursor can uniformly coat the graphite material surface, forming a stable amorphous carbon layer. The thickness of the amorphous carbon layer after carbonization is controlled between 10 and 100 nanometers. This carbon layer can effectively improve the conductivity of the graphite anode, thereby improving the cycle stability and rate performance of the battery. An appropriately thick carbon layer helps to improve the overall performance of the battery, while avoiding an increase in the internal resistance of the anode material due to an excessively thick carbon layer.

[0084] In one possible implementation, the rheological properties of the slurry are monitored in real time using an online rheometer. These rheological properties determine the slurry's viscosity and flowability, which are crucial for subsequent processes such as coating and drying. By dynamically adjusting the shear time and rotor speed, the viscosity and flowability of the slurry can be precisely controlled during preparation, ensuring its stability and uniformity. Real-time monitoring effectively prevents the slurry from becoming too thin or too thick, thus avoiding impacts on the quality of subsequent processes. Feedback adjustments not only improve preparation efficiency but also ensure the consistency of the final electrode material, enhancing battery performance.

[0085] In the spray granulation process, the droplet size distribution has a significant impact on the morphology and performance of the anode material. Real-time monitoring of the droplet size distribution during spray granulation using a laser particle size analyzer allows for immediate adjustment of nozzle parameters and feed pressure based on the monitoring results, ensuring the droplet size distribution remains within the ideal range. An appropriate droplet size distribution can improve the conductivity and ion migration rate of the anode material, thereby enhancing the battery's charge / discharge performance and high-rate performance.

[0086] During the mixing process, temperature distribution significantly affects the uniformity of materials and the reaction rate. Real-time monitoring of temperature distribution during mixing using an infrared thermal imager allows for the timely detection of temperature deviations or inhomogeneities. This enables adjustments to the mixing speed and time based on the monitoring results, ensuring uniform mixing. Appropriate mixing temperature and time contribute to improved material uniformity and prevent material instability caused by excessive temperature fluctuations.

[0087] In the heat treatment process, temperature and atmosphere composition play a decisive role in the structure and properties of the material. Real-time monitoring of temperature and atmosphere composition during heat treatment using thermocouples and gas analyzers allows for precise adjustment of the heating rate and gas flow rate, ensuring the stability and consistency of the heat treatment process. Proper control of temperature and atmosphere helps prevent adverse reactions in graphite anode materials during heat treatment, ensuring material purity and structural stability, and improving battery cycle life and rate performance.

[0088] During the coating process, the adsorption amount of the solution is monitored in real time using a weight sensor, allowing for real-time adjustment of fluidized bed operating conditions and control of coating uniformity and thickness. Coating uniformity directly affects the conductivity of the negative electrode material and the cycle performance of the battery. By monitoring and adjusting the coating process, the quality of each batch of electrode material can be ensured to remain stable, preventing coatings that are too thin or too thick, thereby optimizing battery performance.

[0089] In one possible implementation, the core isotropic graphite is the central component of the material, with its aspect ratio precisely controlled between 1.0 and 1.2. Graphite particles with an aspect ratio less than 1.2 mean that their morphology is close to or near-spherical. This structural feature helps improve the isotropy of the material, meaning that the electrical and ionic conductivity of the material is essentially the same in all directions, thereby enhancing the high-rate performance of the battery. Specifically, this structure helps improve the diffusion rate of lithium ions in the anode material, increasing the charge and discharge efficiency of the battery, especially at high rates (such as 2C and 5C), where it better maintains capacity and performance.

[0090] The thickness of the intermediate composite coating layer is controlled between 0.5 and 5 micrometers. This composite coating layer provides good electronic conductivity for the negative electrode material while mitigating mechanical stress generated during charging and discharging. Through effective coating, the material can avoid internal structural damage caused by excessive current during high-rate discharge, increasing battery life and stability. Furthermore, this layer design buffers the expansion and contraction between graphite particles, preventing material breakage or morphological changes due to prolonged use, thereby improving battery cycle stability.

[0091] The thickness of the amorphous carbon protective layer on the surface is controlled between 10 and 100 nanometers. This amorphous carbon layer provides a protective film for the graphite anode material, helping to improve its surface chemical stability and reduce side reactions caused by the contact between the electrolyte and graphite during battery use. This protective layer design effectively prevents oxidation reactions on the graphite surface, maintains the structural integrity of the electrode, and reduces capacity decay.

[0092] This isotropic modified graphite anode material maintains a capacity retention of over 95% at 2C and no less than 85% at 5C, and retains no less than 97% after 500 cycles. This demonstrates that the material possesses excellent high-rate charge-discharge performance and superior cycle stability, enabling it to withstand prolonged use under rapid charge-discharge conditions. After multiple cycles, the battery retains most of its initial capacity, exhibiting low capacity decay.

[0093] The electrode expansion rate is controlled below 8%, indicating that the material has good volume stability. Graphite is prone to volume expansion during charge and discharge, especially at high discharge rates, which can lead to the shedding of electrode materials inside the battery, thus affecting its lifespan. By rationally designing the core structure and composite coating layer, the electrode expansion rate can be effectively controlled, maintaining the overall structural stability of the battery.

[0094] By precisely controlling the microstructure and surface properties of graphite, this isotropic modified graphite anode material exhibits excellent performance during high-rate charge and discharge processes, and can maintain a long cycle life and good electrode stability, making it suitable for the preparation of high-performance lithium-ion batteries.

[0095] Example

[0096] This embodiment addresses the high-rate performance requirements of lithium-ion batteries in fast-charging scenarios for electric vehicles by providing a specific method for preparing isotropic modified graphite anode materials.

[0097] Step 1: Raw material pretreatment and primary isotropic shaping;

[0098] Natural flake graphite was selected as the raw material, with an initial particle size distribution of D50=25μm, D90=45μm, and D10=8μm. 2000g of natural flake graphite was mixed with 8000g of deionized water in a 50L stirred tank to form a slurry with a solid content of 20%. The slurry was then pumped into a mechanical fluid shearing device (shear chamber volume 5L).

[0099] The core component of the mechanical fluid shearing device is a rotor-stator shearing head. The rotor has a diameter of 150mm, and the stator has an inner diameter of 155mm, forming a narrow gap of 2.5mm. The rotor rotates at a speed of 4500rpm, generating a shearing rate of up to 10 within the gap. 5 s -1 The graphite sheets undergo relative slippage and reorientation under the influence of high-speed turbulence, and the originally parallel graphite sheets gradually become randomized.

[0100] The slurry temperature is maintained at 25±2℃ by the jacket cooling system to prevent the slurry temperature from becoming too high due to shear heat generation.

[0101] The slurry viscosity was controlled at 120±10 mPa·s by adjusting the solids content (measurement conditions: 25℃, shear rate 100s). -1 );

[0102] The shearing time is determined based on real-time monitoring of rheological properties: when the slurry changes from the initial shear thinning index n=0.65 to n=0.95 (close to the Newtonian fluid n=1.0), the shearing process is stopped. In this embodiment, the shearing time is 85 minutes.

[0103] The rotor speed is adjusted in three stages during the process: in the initial stage, 5000 rpm rapidly destroys the original structure; in the middle stage, 4000 rpm optimizes the orientation randomization; and in the later stage, 3500 rpm stabilizes the isotropic structure.

[0104] After shearing, the slurry was subjected to solid-liquid separation using a horizontal centrifuge (3000 rpm, processing capacity 500 L / h). The separated wet material was then transferred to a vacuum drying oven and dried at 80℃ and -0.095 MPa for 12 hours to obtain a primary isotropic graphite intermediate. Image analysis showed that the aspect ratio of the treated graphite particles improved from the initial 3.5±1.2 to 1.15±0.3.

[0105] Step 2: Multi-stage spray granulation and pore structure control;

[0106] Take 1500g of the primary isotropic graphite intermediate obtained in step one and mix it with 8500g of deionized aqueous solution containing 150g of polyvinyl alcohol (degree of polymerization 1700, degree of hydrolysis 88%) to form a uniform suspension with a solid content of 15%.

[0107] The process is carried out using a three-stage tandem spray granulation system:

[0108] The first-stage spray unit uses a pressure nozzle with an orifice diameter of 0.8 mm and a feed pressure of 2.0 MPa to atomize the suspension into droplets with a D50 of 80 μm.

[0109] The second-stage spray unit is located 0.8m downstream of the first stage. It uses a dual-fluid nozzle to uniformly spray a 10% ammonium bicarbonate aqueous solution (pore template agent) onto the surface of the droplets. The mass ratio of template agent to suspension is 1:15.

[0110] The third-stage spray unit is located 0.5m downstream of the second stage. It uses a centrifugal atomizer and covers the droplet surface with a 1% hydroxypropyl methylcellulose aqueous solution (protective film). The mass ratio of the protective film solution to the suspension is 1:20.

[0111] The resulting wet particles were collected and transferred to a temperature-controlled rotary kiln for heat treatment under a nitrogen atmosphere (99.99% purity, 10 L / min flow rate).

[0112] First stage: Increase the temperature to 120℃ at 3℃ / min and hold for 45 minutes to allow the polyvinyl alcohol to partially cross-link and solidify, thus fixing the particle shape;

[0113] The second stage involves heating to 350℃ at a rate of 8℃ / min and holding for 90 minutes to decompose ammonium bicarbonate (NH4HCO3→NH3+CO2+H2O), forming interconnected porous channels with a pore size of 50-500nm inside the particles, with a porosity of approximately 35%.

[0114] The third stage involves heating the polyvinyl alcohol to 650℃ at a rate of 12℃ / min and holding it at that temperature for 150 minutes to completely carbonize the polyvinyl alcohol, forming a robust carbon skeleton that firmly connects the primary isotropic graphite particles, resulting in secondary spherical graphite particles that are porous inside and have a dense outer shell.

[0115] Step 3: Preparation and application of the composite coating layer;

[0116] Preparation of composite coating material: Tin-copper-antimony ternary alloy powder (Sn:Cu:Sb=85:10:5, wt%, melting point 218℃) was mixed with multi-walled carbon nanotubes (outer diameter 8-15nm, length 10-30μm, specific surface area 380m² / g) at a mass ratio of 2:1. The mixing was carried out in an argon-protected glove box (water and oxygen content <0.1ppm).

[0117] The mixed powder was placed in a vacuum induction furnace and heated to 300°C (82°C above the alloy melting point) at a rate of 5°C / min, held at that temperature for 60 minutes, and continuously stirred at 60 rpm to ensure that the molten alloy fully wetted the gaps between the carbon nanotubes. It was then cooled to room temperature at a rate of 3°C / min to obtain the composite coating material.

[0118] 1000g of the secondary spherical graphite particles obtained in step two and 150g of the composite coating material (mass ratio 6.67:1) were added to a high-speed impact mixer (model: HIM-200, volume 10L). Mixing conditions: 1200 rpm, 20 minutes, temperature controlled at 35±5℃ via jacket cooling. During mixing, the composite coating material uniformly and firmly adhered to the surface of the secondary spherical graphite particles under impact and shear forces, achieving a coating rate of up to 98.5%.

[0119] Step 4: Integrating heat treatment and interface strengthening;

[0120] The coated graphite particles were loaded into an alumina crucible and placed in a three-zone tube furnace (each zone is 400 mm long, and the total length is 1200 mm). High-purity argon gas (99.999% purity, flow rate 1.2 L / min) was continuously introduced.

[0121] Fusion heat treatment process:

[0122] First temperature zone: Heat to 250℃ at 8℃ / min and hold for 45 minutes. During this stage, the low-melting-point tin-based alloy component (eutectic phase) in the composite coating partially melts and begins to react with the surface of the graphite particles to form an initial diffusion layer with a thickness of about 50nm;

[0123] Second temperature zone: The temperature is increased to 450℃ at a rate of 3℃ / min and held for 180 minutes. This temperature is higher than the melting point of tin-based alloys (232℃). The molten alloy diffuses with the graphite surface through the solid-liquid interface to form a strong Sn-C chemical bond. At the same time, carbon nanotubes act as a buffer matrix, effectively inhibiting excessive flow and aggregation of the alloy. The interfacial bonding strength can reach 35MPa.

[0124] Cooling stage: The temperature is slowly cooled to room temperature at a rate of 1℃ / min. During the cooling process, a transition layer with a compositional gradient (gradually transitioning from pure carbon to tin-rich region) is formed at the interface, with a thickness of about 800nm, which effectively alleviates thermal stress.

[0125] Step 5: Surface stabilization and carbonization treatment;

[0126] Prepare a 15% phenolic resin ethanol solution as the carbon precursor solution. Add 500g of graphite particles obtained in step four to a fluidized bed coating device (bed diameter 200mm, gas distribution plate porosity 35%), control the airflow velocity at 0.3m / s, and the bed temperature at 60℃. The carbon precursor solution is uniformly sprayed onto the fluidized particle surface using a spray system at a feed rate of 50mL / min, for a total coating time of 30 minutes.

[0127] The coated particles are first pretreated in air at 250°C for 120 minutes to partially cross-link and cure the phenolic resin. Then they are transferred to a vacuum carbonization furnace for carbonization under a nitrogen atmosphere.

[0128] Heat to 250℃ at a rate of 2℃ / min and hold for 60 minutes;

[0129] Increase the temperature to 550℃ at a rate of 4℃ / min and hold for 150 minutes.

[0130] After carbonization, the phenolic resin transforms into an amorphous carbon layer approximately 60 nm thick. This layer fills the microscopic defects on the surface of the composite coating layer, forming a dense protective layer. The amorphous carbon layer and the underlying composite coating layer form a strong bond through carbon atom diffusion, but no significant graphitization occurs, maintaining the functional division of each layer.

[0131] Materials characterization and performance testing;

[0132] The resulting isotropic modified graphite anode material was systematically characterized:

[0133] Structural features:

[0134] Core isotropic graphite: aspect ratio 1.15±0.3, crystal size La=45nm, Lc=28nm;

[0135] Intermediate composite coating layer: 1.2±0.3μm thick, tin-based alloy particles uniformly dispersed in the carbon nanotube network in the form of 20-100nm particles;

[0136] Amorphous carbon protective layer on the surface: thickness 60±15nm, coverage integrity >99%.

[0137] Electrochemical performance (test conditions: coin cell, counter electrode: lithium metal, electrolyte: 1M LiPF6 in EC:DEC = 1:1):

[0138] Initial coulomb efficiency: 95.2% (compared to 92.5% for conventional artificial graphite);

[0139] Reversible specific capacity: 368mAh / g at 0.1C rate;

[0140] Rate performance: 96.8% capacity retention at 2C rate, and 90.1% capacity retention at 5C rate;

[0141] Cycling performance: 98.2% capacity retention after 500 cycles at 1C rate;

[0142] Electrode expansion rate: 5.8% after 100 cycles.

[0143] Microscopic mechanism analysis:

[0144] In-situ X-ray diffraction and ex-situ transmission electron microscopy revealed that the isotropic structure facilitates more uniform lithium-ion insertion and extraction within the graphite, preventing localized stress concentration. The composite coating provides additional lithium storage capacity (the tin-based alloy contributes approximately 120 mAh / g) and improves the electrode's electronic conductivity (from 0.15 S / cm in conventional graphite to 1.28 S / cm). The gradient interface design effectively suppresses interface delamination caused by volume changes in the tin-based alloy during cycling, ensuring long-term cycling stability.

[0145] Basis for key parameter optimization;

[0146] In this embodiment, the determination of each process parameter is based on the experimental optimization and theoretical analysis of the system:

[0147] Relationship between shear time and isotropy: Through the correlation analysis of the material aspect ratio and rate performance under different shear times, it was found that the material has the best rate performance when the aspect ratio reaches 1.15-1.25. Further extending the shear time has limited improvement but significantly increases energy consumption.

[0148] Pore ​​template selection: Ammonium bicarbonate has a moderate decomposition temperature (decomposition begins at about 60℃), the decomposition products are gaseous with no residue, and the decomposition rate can be precisely controlled by temperature, making it suitable for constructing porous structures with uniform pore size distribution.

[0149] Fusion heat treatment temperature setting: The selection of the second temperature zone temperature of 450℃ is based on the following: on the one hand, it should be higher than the melting point of tin-based alloys to ensure sufficient melting and interfacial diffusion, and on the other hand, it should be much lower than the graphitization temperature (generally >2000℃) to avoid damaging the graphite crystal structure, while also considering the stability of carbon nanotubes at this temperature.

[0150] Carbonization temperature optimization: A carbonization temperature of 550℃ ensures that the phenolic resin is fully converted into amorphous carbon (carbonization rate >85%), while avoiding excessive graphitization and loss of its barrier effect on the electrolyte.

[0151] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0152] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing isotropic modified graphite anode materials for high-rate lithium-ion batteries, characterized in that, Includes the following steps: Step 1: Raw material pretreatment and primary isotropic shaping. Natural flake graphite or artificial graphite is selected as raw material. The graphite raw material is mixed with deionized water to form a slurry. The graphite raw material is sheared by mechanical fluid shearing equipment. The shearing intensity and time are controlled to make the aspect ratio of the graphite particles approach 1, thus achieving primary isotropic shaping. Subsequently, the treated graphite slurry is subjected to solid-liquid separation and drying to obtain the primary isotropic graphite intermediate. Step Two: Multi-stage spray granulation and pore structure control. The primary isotropic graphite intermediate obtained in Step One is mixed with a binder solution to form a uniform suspension. The suspension is then treated using a multi-stage spray granulation device. The treatment includes: forming micron-sized droplets through a first-stage spray unit; introducing a pore template agent onto the droplet surface through a second-stage spray unit; and covering the droplet surface with an outer protective film through a third-stage spray unit. Subsequently, a programmed temperature heat treatment is performed under an inert atmosphere. The programmed temperature heat treatment includes: first, raising the temperature at a rate of 1-5°C per minute to 100-150°C to partially crosslink and solidify the binder; then, raising the temperature at a rate of 5-10°C per minute to 300-400°C to remove the pore template agent and form a porous structure; and finally, raising the temperature at a rate of 10-15°C per minute to 600-800°C to completely carbonize the binder, forming secondary spherical graphite particles with internal porous channels and a dense outer shell. Step 3: Preparation and application of composite coating layer. A composite coating material composed of conductive carbon material and tin-based alloy is prepared. The conductive carbon material is selected from graphene, carbon nanotubes or porous carbon. The tin-based alloy is a binary or ternary alloy formed by tin and at least one of copper, silver or antimony. First, the tin-based alloy material and conductive carbon material are mixed in proportion. Under the protection of inert gas, the mixture is heated to above the melting point of the tin-based alloy and kept warm while stirring, so that the liquid alloy can fully wet the conductive carbon material. After cooling, the composite coating material is obtained. Then, the secondary spherical graphite particles obtained in step 2 are mixed with the composite coating material in proportion. The composite coating material is uniformly attached to the surface of the secondary spherical graphite particles by a high-speed impact mixing device. Step 4: Fusion heat treatment and interface strengthening. The coated graphite particles obtained in Step 3 are subjected to fusion heat treatment in a multi-temperature zone tube furnace under inert atmosphere protection. First, the temperature is increased to the first temperature zone at a rate of 8°C per minute and held at 200-300°C. This allows the low-melting-point components in the composite coating to partially melt and form a preliminary bond with the surface of the graphite particles. Then, the temperature is increased to the second temperature zone at a rate of 3°C per minute and held at 400-500°C. The second temperature zone is higher than the melting point of tin-based alloys but lower than the graphitization temperature. This allows the composite coating to form a strong bond with the surface of the graphite particles through interfacial diffusion. Finally, the temperature is cooled to room temperature at a rate of 0.5-2°C per minute. Step 5: Surface stabilization and carbonization treatment. The graphite particles obtained in Step 4 are mixed with the carbon precursor solution. A fluidized bed apparatus is used to uniformly coat the surface of the graphite particles with the carbon precursor solution. Then, carbonization treatment is carried out under an inert atmosphere. The carbonization temperature is controlled to be lower than the graphitization temperature, so that the carbon precursor is transformed into an amorphous carbon layer, forming an amorphous carbon protective layer on the surface.

2. The method for preparing isotropic modified graphite anode material for high-rate lithium-ion batteries according to claim 1, characterized in that, In step one, the mechanical fluid shearing device includes a rotor-stator shearing head. The rotor rotates at high speed, generating strong fluid shearing force and turbulence effect in a narrow gap. The temperature of the slurry is controlled within a certain range by an external cooling or heating system. The viscosity of the slurry is controlled by adjusting the solid content. The aspect ratio of the graphite particles is controlled by adjusting the shearing time, rotor speed, and slurry concentration. During the process, a rheometer is used to monitor the changes in the rheological properties of the slurry in real time. When the slurry changes from obvious shear-thinning behavior to near Newtonian fluid behavior, the shearing process is stopped. Subsequently, a centrifuge or filter is used for solid-liquid separation. The separated solid is dried in a vacuum drying oven. The drying temperature is controlled within a range to avoid graphite oxidation, resulting in a primary isotropic graphite intermediate. The shear head of the mechanical fluid shearing device can generate a high-speed turbulent field, causing graphite particles to slip relative to each other and become randomized in orientation. The shearing time is adjusted based on the initial anisotropy of the graphite raw material.

3. The method for preparing isotropic modified graphite anode material for high-rate lithium-ion batteries according to claim 1, characterized in that, In step two, the first-stage spray unit of the multi-stage spray granulation equipment uses pressure nozzles to atomize the suspension into micron-sized droplets. The droplet size is controlled by adjusting the nozzle orifice diameter and the feed pressure. The second-stage spray unit is located 0.5-1.0 meters downstream of the first-stage spray unit and is used to uniformly spray a pore template agent solution onto the droplet surface. The pore template agent is an organic or inorganic salt that can be decomposed and removed during heat treatment. The third-stage spray unit further coats the droplet surface with a protective polymer solution to prevent the structure formed in the first two stages from being destroyed in subsequent processing. The specific process of the programmed temperature rise heat treatment includes: the first stage is to raise the temperature to 100-150 degrees Celsius at a rate of 1-5 degrees Celsius per minute and hold it for 30-60 minutes to allow the binder to partially cross-link and solidify; the second stage is to raise the temperature to 300-400 degrees Celsius at a rate of 5-10 degrees Celsius per minute and hold it for 60-120 minutes to allow the pore template agent to decompose and volatilize to form a porous structure; the third stage is to raise the temperature to 600-800 degrees Celsius at a rate of 10-15 degrees Celsius per minute and hold it for 120-180 minutes to allow the binder to be completely carbonized to form a carbonaceous skeleton. The binder is a thermoplastic polymer material that undergoes softening, flow, and eventual carbonization during heating. The solid content in the suspension is controlled between 10% and 30% to ensure the smooth operation of spray granulation.

4. The method for preparing isotropic modified graphite anode material for high-rate lithium-ion batteries according to claim 1, characterized in that, In step three, the preparation process of the composite coating material includes: first, mixing tin-based alloy powder and conductive carbon material in a mass ratio of 1:1 to 3:1, mixing under an inert gas protection to prevent material oxidation, placing the uniformly mixed powder in a reactor under vacuum or inert atmosphere protection, heating it to 50-100 degrees Celsius above the melting point of the tin-based alloy at a heating rate of 2-8 degrees Celsius per minute, holding it at that temperature for 30-90 minutes while continuously stirring, so that the molten tin-based alloy fully wets the pores and surface of the conductive carbon material, and then cooling it to room temperature at a cooling rate of 1-5 degrees Celsius per minute to obtain the composite coating material; The mixing process of the high-speed impact mixer includes: mixing secondary spherical graphite particles with composite coating materials at a mass ratio of 10:1 to 5:1, and placing the mixture into the high-speed impact mixer. The mixer utilizes high-speed rotating blades to generate strong impact and shearing action, controlling the rotation speed at 500-2000 rpm, the mixing time at 10-30 minutes, and the mixing temperature at 25-60 degrees Celsius, to ensure that the composite coating material is uniformly and firmly attached to the surface of the secondary spherical graphite particles without damaging the overall structure of the secondary spherical graphite particles.

5. The method for preparing the isotropic modified graphite anode material for high- rate lithium-ion batteries according to claim 1, characterized in that, In step four, the multi-zone tubular furnace for fusion heat treatment has three independently controlled temperature zones. High-purity inert protective gas is continuously introduced into the furnace, and the gas flow rate is controlled at 0.5-2.0 liters / minute to prevent material oxidation. The first temperature range is 200-300 degrees Celsius, and the holding time is 30-60 minutes, so that the low melting point components in the composite coating layer partially melt and undergo preliminary interfacial reaction and atomic diffusion with the surface of the graphite particles. The second temperature range is 400-500 degrees Celsius, and the holding time is 120-240 minutes, so that the molten tin-based alloy can fully contact the surface of the graphite particles and form a strong metallurgical bond through interfacial diffusion. At the same time, the conductive carbon material acts as a buffer matrix to inhibit the excessive flow and aggregation of the tin-based alloy. The cooling rate is slowed down to room temperature at a rate of 0.5-2 degrees Celsius per minute to avoid interface cracking or coating peeling caused by thermal stress generated by rapid cooling. During the fusion heat treatment process, the bonding phase formed at the interface is stabilized and solidified, forming a gradient transition interface structure.

6. The method for preparing the isotropic modified graphite anode material for high- rate lithium ion batteries according to claim 1, characterized in that, In step five, the carbon precursor solution is a phenolic resin solution, a sugar solution, or an asphalt solution, and the carbon precursor can form a dense amorphous carbon layer after heat treatment. The operating conditions of the fluidized bed equipment include: airflow velocity controlled at 0.1-0.5 m / s and temperature controlled at 50-80 degrees Celsius, so that the graphite particles can fully contact the carbon precursor solution in the fluidized state and ensure that the solution is uniformly coated on the particle surface. The specific process of the carbonization treatment includes: first, heating the temperature to 200-300 degrees Celsius at a rate of 1-3 degrees Celsius per minute, holding the temperature for 60-120 minutes to partially crosslink and solidify the carbon precursor, forming a stable temporary protective layer; then heating the temperature to 500-700 degrees Celsius at a rate of 3-6 degrees Celsius per minute, holding the temperature for 120-180 minutes to transform the carbon precursor into an amorphous carbon layer. The carbonization temperature is lower than the graphitization temperature to avoid damaging the already formed composite structure. The amorphous carbon layer fills the micropores and defects on the surface of the composite coating layer, forming a dense protective layer, and at the same time forms a firm bond with the underlying composite coating layer through carbon atom diffusion.

7. The method for preparing the isotropic modified graphite anode material for high- rate lithium-ion batteries according to claim 1, characterized in that, The preparation method also includes performance testing of the final isotropic modified graphite anode material, including electrochemical performance testing and physical performance testing. Electrochemical performance testing was conducted using coin cells, and the test included initial coulombic efficiency, reversible specific capacity, rate capacity retention, and cycle capacity retention. Physical performance testing includes scanning electron microscopy to observe the microstructure of the material, X-ray diffraction to analyze the crystal structure of the material, and specific surface area and porosity analysis to analyze the pore characteristics of the material.

8. The method for preparing isotropic modified graphite anode material for high-rate lithium-ion batteries according to claim 1, characterized in that, In step one, the particle size distribution of the graphite raw material is controlled within the range of 5-50 micrometers, and the solid content of the slurry is controlled between 15% and 25%. In step two, the adhesive is one of polyvinyl alcohol, polyacrylic acid, or polyurethane, and the mass fraction of the adhesive in the suspension is 5%-15%. In step three, the specific surface area of ​​the conductive carbon material is controlled at 100-500 square meters per gram, and the particle size distribution of the tin-based alloy is controlled at 0.1-5 micrometers. In step four, the inert protective gas used in the inert atmosphere is argon or nitrogen, and the gas purity is not less than 99.99%. In step five, the mass fraction of the carbon precursor solution is 10%-20%, and the thickness of the amorphous carbon layer after carbonization is controlled at 10-100 nanometers.

9. The method for preparing the isotropic modified graphite anode material for high- rate lithium-ion batteries according to claim 1, characterized in that, The control of all process parameters in the preparation method is achieved based on real-time monitoring and feedback adjustment. In step one, the rheological properties of the slurry are monitored in real time using an online rheometer, and the shearing time and rotor speed are dynamically adjusted based on the monitoring results; In step two, the droplet size distribution during the spray granulation process is monitored in real time using a laser particle size analyzer, and the nozzle parameters and feed pressure are adjusted based on the monitoring results. In step three, the temperature distribution during the mixing process is monitored in real time using an infrared thermal imager, and the mixing speed and time are adjusted based on the monitoring results; In step four, the temperature and atmosphere composition during the heat treatment process are monitored in real time using thermocouples and a gas analyzer, and the heating rate and gas flow rate are adjusted based on the monitoring results. In step five, the amount of solution adsorbed during the coating process is monitored in real time using a weight sensor, and the fluidized bed operating conditions are adjusted based on the monitoring results.

10. The method for preparing the isotropic modified graphite anode material for high- rate lithium-ion batteries according to claim 1, characterized in that, The isotropic modified graphite anode material obtained by the preparation method has multiple structural features, including an isotropic graphite core, an intermediate composite coating layer, and an amorphous carbon protective layer on the surface. The aspect ratio of the isotropic graphite core is controlled between 1.0 and 1.2 to achieve high isotropy; The thickness of the intermediate composite coating layer is controlled at 0.5-5 micrometers, providing high electronic conductivity and buffering effect; The thickness of the amorphous carbon protective layer on the surface is controlled at 10-100 nanometers to improve the chemical stability and structural integrity of the material surface; The isotropic modified graphite anode material has a capacity retention rate of no less than 95% at 2C rate, no less than 85% at 5C rate, a capacity retention rate of no less than 97% after 500 cycles, and an electrode expansion rate of no more than 8%.

Images